1. Field of the Invention
The present invention relates generally to a fire sensor, and more particularly to a fire sensor with an outer cover for protecting a heat sensing element which detects heat from a hot airflow generated by a fire.
2. Description of the Related Art
As a device for detecting the high temperature or speed of a rise in temperature caused by a fire and issuing an alarm, there is a fire sensor employing a heat detecting element such as a thermistor (Japanese Laid-Open Patent Publication Nos. HEI 9-259376 and HEI 10-188163).
FIG. 14 shows a prior art fire sensor 101. The fire sensor 101 includes a sensor main body 102, a heat detecting element 103 mounted on the sensor main body 102 for detecting heat from a hot airflow generated by a fire, and an outer cover 104 for protecting the heat detecting element 103.
The outer cover 104, as shown in FIG. 15, has a plurality of plate fins 105 for purposes of preventing the hand from touching the heat detecting element 103 and also collecting a hot airflow within the cover 104. The plate fins 105 are disposed toward the cover center.
However, in prior art fire sensors with the outer cover 104 for protecting the heat detecting element 103, a hot airflow cannot be efficiently introduced and collected around the heat sensing element 103 by the plate fins 105 disposed toward the cover center. Because of this, when the outer cover 104 is exposed to a hot airflow, the time lag of a rise in the temperature of the heat detecting element 103 becomes great and there is a problem of reducing a sensitivity to detection.